... Credit: Galileo Project , JPL , NASA Explanation: The Moon's surface is covered with craters, scars of frequent impacts during the early history of the solar system. ... The impact theory of lunar origin can explain, for example, why Moon rocks returned by the Apollo missions have the same isotopic ratios as Earth rocks while the Moon seems deficient in heavy elements like iron. ... Publications with keywords: Moon - origin - impact theory - impact - crater . ... Apollo 17: Shorty Crater Panorama . ...